Magnetic recording media are widely used in various applications, particularly in the computer industry. A portion of a conventional recording medium 1 utilized in disk form in computer-related applications is schematically depicted in FIG. 1 and comprises a non-magnetic substrate 10, typically of metal, e.g., an aluminum-magnesium (Al—Mg) alloy, having sequentially deposited thereon a plating layer 11, such as of amorphous nickel-phosphorus (NiP), a polycrystalline underlayer 12, typically of chromium (Cr) or a Cr-based alloy, a magnetic layer 13, e.g., of a cobalt (Co)-based alloy, a protective overcoat layer 14, typically containing carbon (C), e.g., diamond-like carbon (“DLC”), and a lubricant topcoat layer 15, typically of a perfluoropolyether compound applied by dipping, spraying, etc.
In operation of medium 1, the magnetic layer 13 can be locally magnetized by a write transducer or write head, to record and store data/information. The write transducer creates a highly concentrated magnetic field which alternates direction based on the bits of information being stored. When the local magnetic field produced by the write transducer is greater than the coercivity of the recording medium layer 13, then the grains of the polycrystalline medium at that location are magnetized. The grains retain their magnetization after the magnetic field produced by the write transducer is removed. The direction of the magnetization matches the direction of the applied magnetic field. The pattern of magnetization of the recording medium can subsequently produce an electrical response in a read transducer, allowing the stored medium to be read.
Thin film magnetic recording media are conventionally employed in disk form for use with disk drives for storing large amounts of data in magnetizable form. Typically, one or more disks are rotated on a central axis in combination with data transducer heads. In operation, a typical contact start/stop (“CSS”) method commences when the head begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance from the surface of the disk due to dynamic pressure effects caused by the air flow generated between the sliding surface of the head and the disk. During reading and recording operations, the transducer head is maintained at a controlled distance from the recording surface, supported on a bearing of air as the disk rotates, such that the head can be freely moved in both the circumferential and radial directions, allowing data to be recorded on and retrieved from the disk at a desired position. Upon terminating operation of the disk drive, the rotational speed of the disk decreases and the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the disk. Thus, the transducer head contacts the recording surface whenever the disk is stationary, accelerated from the static position, and during deceleration just prior to completely stopping. Each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic sequence consisting of stopping, sliding against the surface of the disk, floating in air, sliding against the surface of the disk, and stopping.
The air bearing design for the head slider/transducer utilized for CSS-type operation as described above provides an interface between the slider and the disk which prevents damage to the disk over the life of the disk/slider/transducer head system, and provides damping in the event the disk drive system undergoes mechanical shock due to vibrations of external origin. The air bearing also provides the desired spacing between the transducer and the disk surface. A bias force is applied to the slider by a flexure armature in a direction toward the disk surface. This bias force is counter-acted by lifting forces from the air bearing until an equilibrium state is achieved. The slider will contact the disk surface if the rotating speed of the disk is insufficient to cause the slider to “fly”, as during start-up and shut-down phases of the CSS cycle. If the slider contacts a data region of the disk, the data may be lost and the disk permanently damaged.
Referring now to FIG. 2, shown therein in perspective view, is a conventionally configured magnetic hard disk 30 having a CSS (i.e., “landing”) zone 36 and a data (i.e., recording) zone 40. More specifically, FIG. 2 illustrates an annularly-shaped magnetic hard disk 30 including an inner diameter 32 and an outer diameter 34. Adjacent to the inner diameter is an annularly-shaped, inner CSS or “landing” zone 36 (however, the landing zone 36 may, in other instances, be located adjacent the outer diameter 34). When disk 30 is operated in conjunction with a magnetic transducer head (not shown in the drawing), the CSS or “landing” zone 36 is the region where the head makes contact with the disk surface during the above-described start-stop cycles or other intermittent occurrences. In FIG. 2, the radially outer edge of the CSS or “landing” zone 36 is indicated by line 38, which is the boundary between CSS zone 36 and data zone 40 where information in magnetic form is stored within the magnetic recording medium layer of disk 30.
It is generally considered desirable for reliably and predictably performing reading and recording operations, and essential for obtaining high areal density magnetic recording, that the transducer head be maintained as close to the disk surface as possible in order to minimize its flying height. Thus, a smooth disk surface is preferred, as well as a smooth opposing surface of the transducer head, thereby permitting the head and the disk to be positioned in very close proximity, with an attendant increase in predictability and consistent behavior of the air bearing supporting the transducer head during motion. However, if the head surface and the recording surface are too flat, the precision match of these surfaces gives rise to friction and “stiction” at the disk surface which causes the transducer head to adhere to the surface, particularly after periods of non-use, thereby making it more difficult for the transducer head to initiate movement therefrom. Excessive stiction and friction during the start-up and stopping phases of the above-described cyclic sequence causes wear of the transducer and disk surfaces, eventually leading to what is referred to as “head crash”. Another drawback associated with smooth disk surfaces is lack of durability resulting from the very small amount of lubricant which is retained thereon. Thus, there are competing goals of minimizing transducer head flying height (as by the use of smooth surfaces) and reducing transducer head/disk friction (as by avoiding use of smooth surfaces).
Conventional practices for addressing these apparent competing objectives include providing at least the CSS or “landing” zone of the magnetic disk recording medium with a roughened surface to reduce transducer head/disk friction and stiction by a number of different techniques generally known as “texturing”. Referring again to FIG. 1, current texturing techniques (see, e.g., U.S. Pat. Nos. 5,062,021 and 5,108,781) include, inter alia, circumferential polishing and localized laser heating of the surface of the disk substrate 10 (e.g., of Al—Mg alloy) to create thereon a texture pattern comprising a plurality of spaced apart projections (“bumps”) prior to deposition thereon of a layer stack comprised of plating layer 12, polycrystalline seed or underlayer 12, magnetic layer 13, protective overcoat 14, and lubricant topcoat 15, wherein the textured surface of the underlying disk substrate 10 is substantially replicated in the subsequently deposited, overlying layers. According to such methodology, by providing a textured surface in at least the CSS or “landing” zone, the transducer head is able to rest and slide on the peaks of the projections or “bumps” during starting and stopping, thereby reducing the area of contact between the transducer head and the magnetic medium. As a consequence of the reduced area of contact in the CSS or “landing” zone, the amount of force necessary to initiate movement of the transducer head is considerably reduced. An additional advantage provided by the textured disk surface is the ability to retain a greater amount of lubricant, thereby further increasing disk durability by reducing friction and stiction.
A variety of possible configurations of the textured surface approach for reducing stiction and friction between the transducer head and the disk surface are possible, including texturing only the CSS or “landing” zone, wherein specular smoothness of the data zone is retained for permitting high bit density recording by allowing for very low head flying height; texturing the entire disk surface, i.e., the CSS and data zones, whereby friction and stiction reduction is provided in the data zone in addition to the CSS zone; and separately (i.e., differently) textured CSS and data zones, with and without a transition zone between the differently textured zones, wherein the texturing is optimized for each type of zone to maximize both recording characteristics and mechanical durability.
As indicated above, current methodology for selective texturing of the CSS or landing zone of disk-shaped recording media utilizes localized laser heating of the substrate surface to effect melting of the substrate material, which upon re-solidification results in the formation of protrusions, termed “laser bumps” on the disk surface. The bumps dramatically reduce the real area of contact over that which is obtained in the absence of the bumps, which reduced area of contact has a significant impact on the stiction and friction behavior of the head-disk interface. However, texturing of the CSS or landing zone according to the conventional laser texturing process entails a number of disadvantages, including:
(1) currently available lasers cannot texture glass or glass-based substrates, and a sizable capital investment would be required to develop and manufacture lasers and laser systems suitable for rapid, economical (i.e., cost-effective) texturing of glass or glass-based substrates;
(2) the “laser bumps” produced according to conventional laser-based methodology protrude from the disk surface, which protrusions can interfere with the operation of the flying head at very small head-disk spacings;
(3) laser texturing performed according to conventional practices results in a reduction in the width of the recording band by several tens of mils, due to the inherent mechanical “slop” of the laser texture process; and
(4) the laser texture is not precisely aligned with the data tracks because the latter are not written at the same time the laser bumps are formed, which lack of precise alignment limit the width of the recording band.
Also as indicated above, disk drives typically comprise a magnetic head assembly mounted on the end of a support or actuator arm which positions the head radially over the disk surface. If the actuator arm is held stationary, the magnetic head assembly will pass over a circular path on the disk surface known as a track, and information can be read from or written to that track. Each concentric track has a unique radius, and reading and writing information from or to a specific track requires the magnetic head to be located above the track. By moving the actuator arm, the magnetic head assembly is moved radially over the disk surface between tracks.
The disk drive must be able to differentiate between tracks on the disk and to center the magnetic head over any particular track. Most disk drives use embedded “servo patterns” of magnetically recorded information on the disk. The servo patterns are read by the magnetic head assembly to inform the disk drive of the track location. Tracks typically include both data sectors and servo patterns. Each data sector contains a header followed by a data section. The header may include synchronization information to synchronize various timers in the disk drive to the speed of disk rotation, while the data section is used for recording data. Typical servo patterns are described in, for example, U.S. Pat. No. 6,086,961, the disclosure of which is incorporated herein by reference.
Servo patterns are usually written on the disk during manufacture of the disk drive, after the drive is assembled and operational. The servo pattern information, and particularly the track spacing and centering information, needs to be located very precisely on the disk surface. However, at the time the servo patterns are written, there are no reference locations on the disk surface which can be perceived by the disk drive. Accordingly, a highly specialized device known as a “servo-writer” is used during writing of the servo-patterns. Largely because of the locational precision needed, servo-writers are expensive, and servo-writing is a time-consuming process.
A process for forming servo patterns involves use of standard lithographic techniques to remove magnetic material from the magnetic recording layer or by creating recessed zones or valleys in the substrate prior to deposition of the magnetic material. In the former case, the magnetic recording material is etched or ion milled through a resist mask to leave a system of valleys which are void of magnetic material. In the latter case, the magnetic film, which is applied to the textured substrate including recessed zones or valleys, is spaced far enough away from the recording head such that the magnetic flux emanating from the recording head does not sufficiently write the magnetic medium. Servo track information is conveyed by utilizing the difference in magnetic flux at the boundary between the elevated portions and the valleys of the pattern. However, the lithographic processing required for patterning disadvantageously incurs considerable expense inconsistent with the requirements of cost-effective mass production of disk media.
An approach (utilized by Sony Corp. in the manufacture of “PERM” disks) designed to avoid traditional servo-writing has been to injection mold or stamp servo patterns on a polymer-based substrate disk. A constant thickness layer of magnetic recording material is then applied over the entire disk surface, including the depressions and protrusions of the servo patterns. After all of the constituent layers of the medium have been applied to the disk, a magnetic bias is recorded on the servo patterns. For example, a first magnetic field may magnetically initialize the entire disk at a one setting. Then a second magnetic field, located at the surface of the disk and e.g., provided by the magnetic head of the disk drive, is used to magnetize the protruding portions of the servo patterns relative to the depressions. Because the protrusions are closer than the depressions to the magnetic initialization, the magnetization carried by the protrusions may be different than the magnetization carried by the depressions. When read, the resulting disk servo patterns show magnetic transitions between the depressions and the protrusions.
Meanwhile, the continuing trend toward manufacture of very high areal density magnetic recording media at reduced cost provides impetus for the development of lower cost materials, e.g., polymers, glass, ceramics, and glass-ceramics composites as replacements for the conventional Al alloy-based substrates for magnetic disk media. However, poor mechanical and tribological performance, track mis-registration (“TMR”), and poor flyability have been particularly problematic in the case of polymer-based substrates fabricated as to essentially copy or mimic conventional hard disk design features and criteria. On the other hand, glass, ceramic, or glass-ceramic materials are attractive candidates for use as substrates for very high areal density disk recording media because of the requirements for high performance of the anisotropic thin film media and high modulus of the substrate. However, the extreme difficulties encountered with grinding and lapping of glass, ceramic, and glass-ceramic composite materials have limited their use to applications requiring more robust disk drives, such as mobile disk drives for “notebook”-type computers.
Attempts to achieve a desired surface topography on glass, ceramic, or glass-ceramic composite substrates, whether for the data or landing zones, have been unsuccessful due to their extreme hardness (e.g., glass substrates have a Knoop hardness greater than about 760 kg/mm2 compared with about 550 kg/mm2 for Al alloy substrates with NiP plating layers). In addition, the low flowability and extreme hardness of these substrate materials effectively precludes formation of CSS landing zone patterns and servo patterns in the surfaces thereof by injection molding or stamping, as has been performed with polymer-based substrates.
In view of the above, there exists a need for improved methodology and means for rapidly, accurately, and cost-effectively texturing the surfaces of disk substrates for magnetic recording media, which substrates may be constituted of conventional metal-based materials, such as Al-based alloys, or of very hard materials, such as of glass, glass-ceramic, or ceramic, wherein at least one surface of the disk is provided with a patterned CSS or landing zone for optimizing tribological properties when utilized with flying head read/write transducers/heads operating at very low flying heights, and wherein the data zone of the disk is provided with a servo pattern. More specifically, there exists a need for an improved means and methodology for mechanically impressing patterns, e.g., landing zone patterns, as well as servo patterns, by embossing a surface of a substrate for a magnetic recording medium, which substrate may be comprised of a conventional metal-based material or of a very hard material, such as a glass, ceramic, or glass-ceramic composite material. In addition, there exists a need for improved, high areal density magnetic recording media including a substrate having a CSS or landing zone and servo patterns integrally formed therewith, as by embossing.
The present invention addresses and solves problems and difficulties attendant upon the use of conventional surface texturing techniques, e.g., laser texturing, for patterning landing zones and forming servo patterns in various substrate materials utilized in the manufacture of very high areal density magnetic recording media, particularly very hard materials, such as of glass, ceramics, and glass-ceramics, while maintaining full capability with substantially all aspects of conventional automated manufacturing technology for the fabrication of thin-film magnetic media. Further, the methodology and means afforded by the present invention enjoy diverse utility in the manufacture of various other devices and media requiring formation of patterned surfaces by embossing.